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SubjectRe: [PATCH 3/3] virtio: fix endianness check for vhost support
On Tue, Mar 01, 2016 at 04:49:38PM +0000, Andre Przywara wrote:
> Currently we deny any VHOST_* functionality if the architecture
> supports guests with different endianness than the host. Most of the
> time even on those architectures the endianness of guest and host are
> the same, though, so we are denying the glory of VHOST needlessly.
> Switch from compile time determination to a run time scheme, which
> takes the actual endianness of the guest into account.
> For this we change the semantics of VIRTIO_ENDIAN_HOST to return the
> actual endianness of the host (the endianness of kvmtool at compile
> time, really). The actual check in vhost_net now compares this against
> the guest endianness.
> This enables vhost support on ARM and ARM64.
>
> Signed-off-by: Andre Przywara <andre.przywara@arm.com>
> ---
> include/kvm/virtio.h | 9 +++++++--
> virtio/net.c | 2 +-
> 2 files changed, 8 insertions(+), 3 deletions(-)
>
> diff --git a/include/kvm/virtio.h b/include/kvm/virtio.h
> index 768ee96..66530fd 100644
> --- a/include/kvm/virtio.h
> +++ b/include/kvm/virtio.h
> @@ -17,10 +17,15 @@
> #define VIRTIO_PCI_O_CONFIG 0
> #define VIRTIO_PCI_O_MSIX 1
>
> -#define VIRTIO_ENDIAN_HOST 0
> #define VIRTIO_ENDIAN_LE (1 << 0)
> #define VIRTIO_ENDIAN_BE (1 << 1)
>
> +#if __BYTE_ORDER__ == __ORDER_LITTLE_ENDIAN__
> +#define VIRTIO_ENDIAN_HOST VIRTIO_ENDIAN_LE
> +#else
> +#define VIRTIO_ENDIAN_HOST VIRTIO_ENDIAN_BE
> +#endif

pci.h already uses __BYTE_ORDER and __LITTLE_ENDIAN, so we should at least
be consistent here.

Will

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